Gelation of deoxyhemoglobin S within an SS erythrocyte is believed to result in the cell deformity and membrane rigidity characteristic of a sickled SS erythrocyte. To assess the antisickling potential of various agents which might be competitive inhibitors of deoxyhemoglobin S aggregation, we used a kinetic-solubility assay for hemoglobin S. We found that aromatic amino acids, phenylatanine-like compounds and some phenylalanine containing di- and tri- peptides significantly inhibit gelation of deoxyhemoglobin S. Surprisingly, peptides from the Bs sequence enhanced gelation. 13C NMR was used to develop another gelation assay which would also be useful for whole cells. Using new decoupling procedures to quantitate the mass fraction of freely rotating and immobilized hemoglobin molecules, the 13C NMR measurements indicate a smaller percent of polymerized hemolgobin S than predicted by the kinetic-solubility assay. The reasons for this discrepancy are under study. Both assays are valuable tools for studying hemoglobin interactions in solution and in situ and for searching for a therapeutic antisickling agent.